During a warm summer day in the city, people try to escape the city heat by going to the parks. I live in Amsterdam and on entering the Vondelpark at night I can smell the humidity of the trees and feel the coolness, the temperature dropping by several degrees. The falling temperature at night causes the air moisture to precipitate on plants. In desert regions, this is the only water plants may get for years. The moisture in the air is very important for the daily plant-air exchange cycle of water.

Now is the temperature really lower in areas with a rich plant life?

Anyone would argue that the trees and plants keep the park cooler and that the "concrete jungle" easily heats up. No question on this, cities even create microclimates, the urban heat island effect, local warmer zones that influence weather patterns, just like big lakes and rivers or mountain ridges have an effect. But why in the popular press do we always relate global warming mainly to CO₂ increase and other men-made gasses but ignore land use?

Land use is the stripping of densely grown natural areas from most of the rich plant live for agriculture, suburbia with widely spaced houses or industrial areas, or cities, reducing the volume of trees and plants down to a few percent only. Not only the vegetation is reduced but the run-off of water is increased and storage capacity of water is reduced by deeply ploughed fields, hard ground (like in ski areas in the mountains), sewage systems that direct the rain water straight to the stream, and channelling of and dikes along rivers. This reduces the volume of water present in the environment and the risk in floods. Examples are the massive floods along the Mississippi River in the USA in 199x and the Rhine in Europe in 199x caused by levies (dikes) and reduced overflow regions, Central Europe in August 2002 and China in the past few years.

In many countries especially the USA, cities use much more land than needed for industrial and housing development caused by poor planning and driven by short-term return. Sprawling cities are indeed cheaper to build. Later on, the wasteland created causes typical city problems, starting with congested roads during rush hour traffic to nightly crime in neglected, run-down areas.

Agriculture and forest farming is gradually taking over the earth and the percentage of original, densely grown areas is diminishing. We never replace natural areas with equivalent amount of vegetation, although some countries are trying, e.g. the massive reforestation in Spain since the seventies.

Desert regions may be dry and warm in the summer but in unspoiled wilderness there is plenty of growth and animal life. However, in many areas, this changed with human intervention over the past 10000 years. Prime examples are the Middle East and the Sahara.

The Middle East, the so-called "Fertile Crescent" ranging from Palestine, through Turkey and Syria to Mesopotamia and Persia, is the area where most of the current farm animals were first domesticated. The large increase in human population around 8000 years BC had a close relation with the rapid increase in herding animals and agriculture. It started with keeping wild deer gradually replaced by domesticated goats, quickly followed by sheep and cows. Later on pigs and chickens were kept and finally horses. In many areas the population increase was so large they had to settle in villages and turn to agriculture as this is more efficient.

Goats and to a lesser extend sheep thrive well in relative dry regions as they can almost eat anything and without careful control, can destroy the vegetation except for the few very tough scrubs.

In places like Oman the vegetation is mostly stripped but you still see goats that live on the few remaining plants and scrubs. If these animals were kept out by restricting the freedom to roam, the vegetation would be denser. In countries like Spain this is well known and goats are only allowed to eat in certain areas preventing them to destroy the plant life.

The population pressure on the region is now high. The height of the Persian civilisation around 350 BC had an empire of only 12 million people and covered the entire Middle East area including the central Asian Muslim states like Kazakstan and Turkmenistan.

Until 5000 BC, the Sahara dessert was a savannah region with typical big wild animals like lions and elephants. A major climate changes did take place around 5000 BC with the rise of the average sea level by 100 meters and we now think that this forced the increasing number of herds men in the Sahara savannah to move to Europe. The Basques, Etrusks and Cretensers are now thought to come from the Sahara region based on DNA studies. Now is the climate purely a global phenomenon or is it influenced by people? Indeed the rapid melting of the giant Agassiz ice sheet that covered most of Canada and is similar in size to Greenland had an influence but more likely the fragile savannah region in the Sahara was overgrazed and turned to dessert and this could have increasing the effect.

Even during the antique times of the Greece and Romans, Northern Africa still had patches of savannah and was known as the wheat belt. Cartage had an army with elephants and lions and gazelle where common all through Northern Africa and the Middle East. The average temperature variations were similar to now with 1000-year cycles between warmer and colder, making e.g. 2000-2500 BC (height of Egyptian civilisation), 0 AD (height of Roman civilisation), 1000 AD (height of Viking and Arab civilisations) warm periods similar to now.

The current, dry Sahara region has a major impact on climate on earth. Sand dust carried by the strong Southwest pasaat winds in the summer settles even in the Caribbean killing the corrals which are major CO₂ sinks and is visible as huge clouds on satellite pictures.

A recent example are the deserts forming in Turkmenistan by overusage of water for agriculture. The Aral lake disappeared for 70% and the area around the former lake is now a dry dusty desert.

The amount of water and moisture that used to be stored in the warm regions like the Sahara and the Middle East is now minimal and the average temperature is several degrees of warmer. The main cause is thought to be land use by herding and agriculture. This has a major impact on the earth climate.